Benzene
and Human HealthWhat
is benzene? Benzene,
also known as benzol, is a colorless liquid with a sweet odor. Benzene evaporates
into air very quickly and dissolves slightly in water. Benzene is highly flammable.
Most people can begin to smell benzene in air at 1.5-4.7 parts of benzene per
million parts of air (ppm) and smell benzene in water at 2 ppm. Most people can
begin to taste benzene in water at 0.5-4.5 ppm. One part per million is approximately
equal to one drop in 40 gallons. Benzene is found in air, water, and soil. Benzene
comes from both industrial and natural sources. Industrial
Sources and Uses. Benzene was first discovered and isolated from coal tar
in the 1800s. Today, benzene is made mostly from petroleum. Because of its wide
use, benzene ranks in the top 20 in production volume for chemicals produced in
the United States. Various industries use benzene to make other chemicals, such
as styrene (for StyrofoamŪ and other plastics), cumene (for various resins), and
cyclohexane (for nylon and synthetic fibers). Benzene is also used in the manufacturing
of some types of rubbers, lubricants, dyes, detergents, drugs, and pesticides.
Natural
Sources. Natural sources of benzene, which include gas emissions from volcanoes
and forest fires, also contribute to the presence of benzene in the environment.
Benzene is also present in crude oil and gasoline and cigarette smoke. What
happens to benzene when it enters the environment? Benzene
is commonly found in the environment. Industrial processes are the main sources
of benzene in the environment. Benzene levels in the air can be elevated by emissions
from burning coal and oil, benzene waste and storage operations, motor vehicle
exhaust, and evaporation from gasoline service stations. Tobacco smoke is another
source of benzene in air, particularly indoors. Industrial discharge, disposal
of products containing benzene, and gasoline leaks from underground storage tanks
release benzene into water and soil. Benzene
can pass into air from water and soil surfaces. Once in the air, benzene reacts
with other chemicals and breaks down within a few days. Benzene in the air can
also be deposited on the ground by rain or snow. Benzene
in water and soil breaks down more slowly. Benzene is slightly soluble in water
and can pass through the soil into underground water. Benzene in the environment
does not build up in plants or animals. How
might I be exposed to benzene? Everyone
is exposed to a small amount of benzene every day. You are exposed to benzene
in the outdoor environment, in the workplace, and in the home. Exposure of the
general population to benzene mainly occurs through breathing air that contains
benzene. The major sources of benzene exposure are tobacco smoke, automobile service
stations, exhaust from motor vehicles, and industrial emissions. Vapors (or gases)
from products that contain benzene, such as glues, paints, furniture wax, and
detergents, can also be a source of exposure. Auto exhaust and industrial emissions
account for about 20% of the total national exposure to benzene. About half of
the exposure to benzene in the United States results from smoking tobacco or from
exposure to tobacco smoke. The average smoker (32 cigarettes per day) takes in
about 1.8 milligrams (mg) of benzene per day. This amount is about 10 times the
average daily intake of benzene by nonsmokers. Measured
levels of benzene in outdoor air range from 0.02 to 34 parts of benzene per billion
parts of air (ppb) (1 ppb is 1,000 times less than 1 ppm). People living in cities
or industrial areas are generally exposed to higher levels of benzene in air than
those living in rural areas. Benzene levels in the home are usually higher than
outdoor levels. People may be exposed to higher levels of benzene in air by living
near hazardous waste sites, petroleum refining operations, petrochemical manufacturing
sites, or gas stations. For
most people, the level of exposure to benzene through food, beverages, or drinking
water is not as high as through air. Drinking water typically contains less than
0.1 ppb benzene. Benzene has been detected in some bottled water, liquor, and
food. Leakage from underground gasoline storage tanks or from landfills and hazardous
waste sites that contain benzene can result in benzene contamination of well water.
People with benzene-contaminated tap water can be exposed from drinking the water
or eating foods prepared with the water. In addition, exposure can result from
breathing in benzene while showering, bathing, or cooking with contaminated water.
Individuals
employed in industries that make or use benzene may be exposed to the highest
levels of benzene. As many as 238,000 people may be occupationally exposed to
benzene in the United States. These industries include benzene production (petrochemicals,
petroleum refining, and coke and coal chemical manufacturing), rubber tire manufacturing,
and storage or transport of benzene and petroleum products containing benzene.
Other workers who may be exposed to benzene include coke oven workers in the steel
industry, printers, rubber workers, shoe makers, laboratory technicians, firefighters,
and gas station employees. How
can benzene enter and leave my body? Benzene
can enter your body through your lungs, gastrointestinal tract, and across your
skin. When you are exposed to high levels of benzene in air, about half of the
benzene you breathe in passes through the lining of your lungs and enters your
bloodstream. When you are exposed to benzene in food or drink, most of the benzene
you take in by mouth passes through the lining of your gastrointestinal tract
and enters your bloodstream. A small amount will enter your body by passing through
your skin and into your bloodstream during skin contact with benzene or benzene-containing
products. Once in the bloodstream, benzene travels throughout your body and can
be temporarily stored in the bone marrow and fat. Benzene is converted to products,
called metabolites, in the liver and bone marrow. Some of the harmful effects
of benzene exposure are caused by these metabolites. Most of the metabolites of
benzene leave the body in the urine within 48 hours after exposure. How
can benzene affect my health? Scientists
use many tests to protect the public from harmful effects of toxic chemicals and
to find ways for treating persons who have been harmed. One
way to learn whether a chemical will harm people is to determine how the body
absorbs, uses, and releases the chemical. For some chemicals, animal testing may
be necessary. Animal testing may also help identify health effects such as cancer
or birth defects. Without laboratory animals, scientists would lose a basic method
for getting information needed to make wise decisions that protect public health.
Scientists have the responsibility to treat research animals with care and compassion.
Scientists must comply with strict animal care guidelines because laws today protect
the welfare of research animals. After
exposure to benzene, several factors determine whether harmful health effects
will occur, as well as the type and severity of such health effects. These factors
include the amount of benzene to which you are exposed and the length of time
of the exposure. Most information on effects of long-term exposure to benzene
are from studies of workers employed in industries that make or use benzene. These
workers were exposed to levels of benzene in air far greater than the levels normally
encountered by the general population. Current levels of benzene in workplace
air are much lower than in the past. Because of this reduction and the availability
of protective equipment such as respirators, fewer workers have symptoms of benzene
poisoning. Brief
exposure (5-10 minutes) to very high levels of benzene in air (10,000-20,000 ppm)
can result in death. Lower levels (700-3,000 ppm) can cause drowsiness, dizziness,
rapid heart rate, headaches, tremors, confusion, and unconsciousness. In most
cases, people will stop feeling these effects when they are no longer exposed
and begin to breathe fresh air. Eating
foods or drinking liquids containing high levels of benzene can cause vomiting,
irritation of the stomach, dizziness, sleepiness, convulsions, rapid heart rate,
coma, and death. The health effects that may result from eating foods or drinking
liquids containing lower levels of benzene are not known. If you spill benzene
on your skin, it may cause redness and sores. Benzene in your eyes may cause general
irritation and damage to your cornea. Benzene
causes problems in the blood. People who breathe benzene for long periods may
experience harmful effects in the tissues that form blood cells, especially the
bone marrow. These effects can disrupt normal blood production and cause a decrease
in important blood components. A decrease in red blood cells can lead to anemia.
Reduction in other components in the blood can cause excessive bleeding. Blood
production may return to normal after exposure to benzene stops. Excessive exposure
to benzene can be harmful to the immune system, increasing the chance for infection
and perhaps lowering the body's defense against cancer. Long-term
exposure to benzene can cause cancer of the blood-forming organs. This condition
is called leukemia. Exposure to benzene has been associated with development of
a particular type of leukemia called acute myeloid leukemia (AML). The Department
of Health and Human Services has determined that benzene is a known carcinogen
(can cause cancer). Both the International Agency for Cancer Research and the
EPA have determined that benzene is carcinogenic to humans. Exposure
to benzene may be harmful to the reproductive organs. Some women workers who breathed
high levels of benzene for many months had irregular menstrual periods. When examined,
these women showed a decrease in the size of their ovaries. However, exact exposure
levels were unknown, and the studies of these women did not prove that benzene
caused these effects. It is not known what effects exposure to benzene might have
on the developing fetus in pregnant women or on fertility in men. Studies with
pregnant animals show that breathing benzene has harmful effects on the developing
fetus. These effects include low birth weight, delayed bone formation, and bone
marrow damage. We
do not know what human health effects might occur after long-term exposure to
food and water contaminated with benzene. In animals, exposure to food or water
contaminated with benzene can damage the blood and the immune system and can cause
cancer. How
can benzene affect children? This
section discusses potential health effects in humans from exposures during the
period from conception to maturity at 18 years of age. Children
can be affected by benzene exposure in the same ways as adults. Benzene can pass
from the mother's blood to a fetus. It is not known if children are more susceptible
to benzene poisoning than adults How
can families reduce the risk of exposure to benzene? If
your doctor finds that you have been exposed to substantial amounts of benzene,
ask whether your children might also have been exposed. Your doctor might need
to ask your state health department to investigate. Gasoline
and cigarette smoke are two main sources of human exposure to benzene. Benzene
exposure can be reduced by limiting contact with these sources. People are exposed
to benzene from both active and passive second hand smoke. Average smokers take
in about 10 times more benzene than nonsmokers each day. Families are encouraged
not to smoke in their house, in enclosed environments, or near their children. Benzene
is a major component of gasoline and used in many manufacturing processes. Increased
levels of benzene can be found at fueling stations, and in air emissions from
manufacturing plants and hazardous waste sites. Living near gasoline fueling stations
or hazardous waste sites may increase exposure to benzene. People are advised
not to have their families play near fueling stations, manufacturing plants, or
hazardous waste sites. Is
there a medical test to determine whether I have been exposed to benzene? Several
tests can show whether you have been exposed to benzene. Some of these tests may
be available at your doctor's office. All of these tests are limited in what they
can tell you. The test for measuring benzene in your breath must be done shortly
after exposure. This test is not very helpful for detecting very low levels of
benzene in your body. Benzene can be measured in your blood. However, because
benzene rapidly disappears in the blood, measurements may be useful only for recent
exposures. In
the body, benzene is converted to products called metabolites. Certain metabolites
of benzene, such as phenol, muconic acid, and S-phenylmercapturic acid can be
measured in the urine. The amount of phenol in urine has been used to check for
benzene exposure in workers. The test is useful only when you are exposed to benzene
in air at levels of 10 ppm or greater. However, this test must also be done shortly
after exposure, and it is not a reliable indicator of how much benzene you have
been exposed to, because phenol is present in the urine from other sources (diet,
environment). Measurements of muconic acid or S phenylmercapturic acid in the
urine are more sensitive and reliable indicators of benzene exposure. The measurement
of benzene in blood or of metabolites in urine cannot be used for making predictions
about whether you will experience any harmful health effects. Blood counts of
all components of the blood and examination of bone marrow are used to determine
benzene exposure and its health effects. For
people exposed to relatively high levels of benzene, complete blood analyses can
be used to monitor possible changes related to exposure. However, blood analyses
are not useful when exposure levels are low. What
recommendations has the federal government made to protect human health? The
federal government develops regulations and recommendations to protect public
health. Regulations can be enforced by law. The EPA, the Occupational Safety and
Health Administration (OSHA), and the Food and Drug Administration (FDA) are some
federal agencies that develop regulations for toxic substances. Recommendations
provide valuable guidelines to protect public health, but cannot be enforced by
law. The Agency for Toxic Substances and Disease Registry (ATSDR) and the National
Institute for Occupational Safety and Health (NIOSH) are two federal organizations
that develop recommendations for toxic substances. Regulations
and recommendations can be expressed as "not-to-exceed" levels, that is, levels
of a toxic substance in air, water, soil, or food that do not exceed a critical
value that is usually based on levels that affect animals; they are then adjusted
to levels that will help protect humans. Sometimes these not-to-exceed levels
differ among federal organizations because they used different exposure times
(an 8-hour workday or a 24-hour day), different animal studies, or other factors.
Recommendations
and regulations are also updated periodically as more information becomes available.
For the most current information, check with the federal agency or organization
that provides it. Some regulations and recommendations for benzene include the
following: EPA
has set 5 ppb as the maximum permissible level of benzene in drinking water. EPA
has set a goal of 0 ppb for benzene in drinking water and in water such as rivers
and lakes because benzene can cause leukemia. EPA estimates that 10 ppb benzene
in drinking water that is consumed regularly or exposure to 0.4 ppb in air over
a lifetime could cause a risk of one additional cancer case for every 100,000
exposed persons. EPA recommends 200 ppb as the maximum permissible level of benzene
in water for short-term exposures (10 days) for children. EPA
requires that the National Response Center be notified following a discharge or
spill into the environment of 10 pounds or more of benzene. OSHA
regulates levels of benzene in the workplace. The maximum allowable amount of
benzene in workroom air during an 8-hour workday, 40-hour workweek is 1 ppm. Because
benzene can cause cancer, NIOSH recommends that all workers wear special breathing
equipment when they are likely to be exposed to benzene at levels exceeding the
recommended (8-hour) exposure limit of 0.1 ppm. Where
can I get more information? If
you have any more questions or concerns, please contact your community or state
health or environmental quality department or: Agency
for Toxic Substances and Disease Registry
Division of Toxicology
1600 Clifton
Road NE, Mailstop F-32
Atlanta, GA 30333
Information
line and technical assistance: Phone:
888-422-8737
FAX: (770)-488-4178 ATSDR
can also tell you the location of occupational and environmental health clinics.
These clinics specialize in recognizing, evaluating, and treating illnesses resulting
from exposure to hazardous substances. To
order toxicological profiles, contact: National
Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Phone: 800-553-6847 or 703-605-6000 References Agency
for Toxic Substances and Disease Registry (ATSDR). 2005. Toxicological
profile for benzene. (Draft for Public
Comment). Atlanta, GA: U.S. Department of Health and Human Services, Public
Health Service.
http://www.atsdr.cdc.gov/toxprofiles/phs3.html |
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